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Variation of the mineral density in cortical bone may serve to keep strain amplitudes within a physiological range

Journal

Bone

Volume | Issue number

55 | 2

Pages (from-to)

391-399

Document type

Article

Faculty

Faculty of Dentistry (ACTA)

Abstract

Within-bone variation in mineral density could be functional. A heterogeneous mineral-density distribution might serve to
maintain habitual amplitudes of bone strain within a non-harmful, i.e., physiological range. Regions of a bone that would
be strained the most on the basis of architecture alone might have a higher mineral density to make them more stiff and resistant
to strain.

We hypothesised that the cortical bone of the rabbit mandible contains such a functional distribution
of mineral density. We thereby expected similar mineral-density patterns in the mandibles of different individuals due to
the shared masticatory function. Secondly, we hypothesised that the highest mineral densities occur in mandibular regions
predicted to be exposed to the largest amplitudes of strain—when taking into account bone architecture only. Mineral-density
maps of the cortical bone of rabbit mandibles were obtained using micro-computed tomography (μCT). The μCT scans of two rabbits
were converted into finite-element models (FEMs). To predict mandibular deformation during biting, these models were loaded
by muscle forces and reaction forces. The forces acted on the condyles and on either the incisal or molar bite point. The
FEMs were assigned a homogeneous material stiffness to calculate the strain amplitudes that would occur when only the architecture
of the mandibular bone would be of influence.

We found the cortical bone-mineral density patterns to be similar in
all six mandibles. The mineral density of the corpus was higher than that of the ramus. A second consistent feature of the
mandibular mineral-density distribution was that the medial ridge of the temporal-muscle insertion groove contained more mineral
than its surrounding regions. The strain amplitudes calculated with the FEMs were variable and did not feature clear corpo-ramal
differences. However, specific mandibular bone sites calculated to be exposed to the largest amplitudes of strain, including
the medial ridge of the temporal-muscle insertion groove, did correspond with high-mineral-density regions. We conclude that,
in the rabbit mandible, the heterogeneous mineral-density distribution might serve to suppress bone-strain amplitudes in regions
architecturally susceptible to the largest deformations during loading.

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